Order this document by UC3842A/D
UC3842A, 43A
UC2842A, 43A
High Performance
Current Mode Controllers
The UC3842A, UC3843A series of high performance fixed frequency
current mode controllers are specifically designed for off–line and dc–to–dc
converter applications offering the designer a cost effective solution with
minimal external components. These integrated circuits feature a trimmed
oscillator for precise duty cycle control, a temperature compensated
reference, high gain error amplifier, current sensing comparator, and a high
current totem pole output ideally suited for driving a power MOSFET.
Also included are protective features consisting of input and reference
undervoltage lockouts each with hysteresis, cycle–by–cycle current limiting,
programmable output deadtime, and a latch for single pulse metering.
These devices are available in an 8–pin dual–in–line plastic package as
well as the 14–pin plastic surface mount (SO–14). The SO–14 package has
separate power and ground pins for the totem pole output stage.
The UCX842A has UYLO thresholds of 16 V (on) and 10 V (off), ideally
suited for off–line converters. The UCX843A is tailored for lower voltage
applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).
•
Trimmed Oscillator Discharge Current for Precise Duty Cycle Control
HIGH PERFORMANCE
CURRENT MODE
CONTROLLERS
N SUFFIX
PLASTIC PACKAGE
CASE 626
8
1
D SUFFIX
PLASTIC PACKAGE
CASE 751A
(SO–14)
14
1
•
•
•
•
•
•
•
•
Current Mode Operation to 500 kHz
Automatic Feed Forward Compensation
Latching PWM for Cycle–By–Cycle Current Limiting
Internally Trimmed Reference with Undervoltage Lockout
High Current Totem Pole Output
Undervoltage Lockout with Hysteresis
Low Startup and Operating Current
Direct Interface with Motorola SENSEFET Products
PIN CONNECTIONS
Compensation 1
Voltage Feedback 2
Current Sense 3
RT/CT 4
(Top View)
8
7
6
5
Vref
VCC
Output
Gnd
Compensation
NC
Voltage Feedback
NC
Current Sense
1
2
3
4
5
6
7
(Top View)
14 Vref
13 NC
12 VCC
11 VC
10 Output
9
8
Gnd
Power Ground
Simplified Block Diagram
VCC
Vref
8(14)
R
R
RTCT
4(7)
Voltage
Feedback
Input
2(3)
Output
Compensation
1(1)
+
–
NC
RT/CT
7(12)
5.0V
Reference
Vref
Undervoltage
Lockout
Oscillator
Latching
PWM
Error
Amplifier
VCC
Undervoltage
Lockout
VC
7(11)
Output
6(10)
Power
Ground
5(8)
Current
Sense
3(5) Input
ORDERING INFORMATION
Device
UC3842AD
UC3843AD
UC3842AN
UC3843AN
UC2842AD
UC2843AD
UC2842AN
UC2843AN
©
Motorola, Inc. 1996
Operating
Temperature Range
Package
SO–14
TA = 0° to +70°C
SO–14
Plastic
Plastic
SO–14
Gnd
5(9)
TA = – 25° to +85°C
SO–14
Plastic
Plastic
Rev 1
Pin numbers in parenthesis are for the D suffix SO–14 package.
MOTOROLA ANALOG IC DEVICE DATA
1
UC3842A, 43A UC2842A, 43A
MAXIMUM RATINGS
Rating
Total Power Supply and Zener Current
Output Current, Source or Sink (Note 1)
Output Energy (Capacitive Load per Cycle)
Current Sense and Voltage Feedback Inputs
Error Amp Output Sink Current
Power Dissipation and Thermal Characteristics
D Suffix, Plastic Package
Maximum Power Dissipation @ TA = 25°C
Thermal Resistance, Junction–to–Air
N Suffix, Plastic Package
Maximum Power Dissipation @ TA = 25°C
Thermal Resistance, Junction–to–Air
Operating Junction Temperature
Operating Ambient Temperature
UC3842A, UC3843A
UC2842A, UC2843A
Storage Temperature Range
Symbol
(ICC + IZ)
IO
W
Vin
IO
Value
30
1.0
5.0
– 0.3 to + 5.5
10
Unit
mA
A
µJ
V
mA
PD
R
θJA
PD
R
θJA
TJ
TA
862
145
1.25
100
+ 150
0 to + 70
– 25 to + 85
mW
°C/W
W
°C/W
°C
°C
Tstg
– 65 to + 150
°C
ELECTRICAL CHARACTERISTICS
(VCC = 15 V, [Note 2], RT = 10 k, CT = 3.3 nF, TA = Tlow to Thigh [Note 3],
unless otherwise noted.)
UC284XA
Characteristics
REFERENCE SECTION
Reference Output Voltage (IO = 1.0 mA, TJ = 25°C)
Line Regulation (VCC = 12 V to 25 V)
Load Regulation (IO = 1.0 mA to 20 mA)
Temperature Stability
Total Output Variation over Line, Load, Temperature
Output Noise Voltage (f = 10 Hz to 10 kHz, TJ = 25°C)
Long Term Stability (TA = 125°C for 1000 Hours)
Output Short Circuit Current
OSCILLATOR SECTION
Frequency
TJ = 25°C
TA = Tlow to Thigh
Frequency Change with Voltage (VCC = 12 V to 25 V)
Frequency Change with Temperature
TA = Tlow to Thigh
Oscillator Voltage Swing (Peak–to–Peak)
Discharge Current (Vosc = 2.0 V)
TJ = 25°C
TA = Tlow to Thigh
fosc
47
46
∆f
osc/
∆
V
∆f
osc/
∆
T
Vosc
Idischg
7.5
7.2
8.4
–
9.3
9.5
7.5
7.2
8.4
–
9.3
9.5
–
–
–
52
–
0.2
5.0
1.6
57
60
1.0
–
–
47
46
–
–
–
52
–
0.2
5.0
1.6
57
60
1.0
–
–
%
%
V
mA
kHz
Vref
Regline
Regload
TS
Vref
Vn
S
ISC
4.95
–
–
–
4.9
–
–
– 30
5.0
2.0
3.0
0.2
–
50
5.0
– 85
5.05
20
25
–
5.1
–
–
– 180
4.9
–
–
–
4.82
–
–
– 30
5.0
2.0
3.0
0.2
–
50
5.0
– 85
5.1
20
25
–
5.18
–
–
– 180
V
mV
mV
mV/°C
V
µV
mV
mA
Symbol
Min
Typ
Max
Min
UC384XA
Typ
Max
Unit
NOTES:
1. Maximum Package power dissipation limits must be observed.
2. Adjust VCC above the Startup threshold before setting to 15 V.
3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible
Tlow =
–20°C
for UC3842A, UC3843A
Thigh = +70°C for UC3842A, UC3843A
Tlow =
–25°C for UC2842A, UC2843A
Thigh =
+85°C for UC2842A, UC2843A
2
MOTOROLA ANALOG IC DEVICE DATA
UC3842A, 43A UC2842A, 43A
ELECTRICAL CHARACTERISTICS
(VCC = 15 V, [Note 2], RT = 10 k, CT = 3.3 nF, TA = Tlow to Thigh [Note 3],
unless otherwise noted.)
UC284XA
Characteristics
ERROR AMPLIFIER SECTION
Voltage Feedback Input (VO = 2.5 V)
Input Bias Current (VFB = 2.7 V)
Open Loop Voltage Gain (VO = 2.0 V to 4.0 V)
Unity Gain Bandwidth (TJ = 25°C)
Power Supply Rejection Ratio (VCC = 12 V to 25 V)
Output Current
Sink (VO = 1.1 V, VFB = 2.7 V)
Source (VO = 5.0 V, VFB = 2.3 V)
Output Voltage Swing
High State (RL = 15 k to ground, VFB = 2.3 V)
Low State (RL = 15 k to Vref, VFB = 2.7 V)
CURRENT SENSE SECTION
Current Sense Input Voltage Gain (Notes 4 & 5)
Maximum Current Sense Input Threshold (Note 4)
Power Supply Rejection Ratio
VCC = 12 to 25 V (Note 4)
Input Bias Current
Propagation Delay (Current Sense Input to Output)
OUTPUT SECTION
Output Voltage
Low State (ISink = 20 mA)
Low State
(ISink = 200 mA)
High State (ISink = 20 mA)
High State
(ISink = 200 mA)
Output Voltage with UVLO Activated
VCC = 6.0 V, ISink = 1.0 mA
Output Voltage Rise Time (CL = 1.0 nF, TJ = 25°C)
Output Voltage Fall Time (CL = 1.0 nF, TJ = 25°C)
UNDERVOLTAGE LOCKOUT SECTION
Startup Threshold
UCX842A
UCX843A
Minimum Operating Voltage After Turn–On
UCX842A
UCX843A
PWM SECTION
Duty Cycle
Maximum
Minimum
TOTAL DEVICE
Power Supply Current (Note 2)
Startup:
(VCC = 6.5 V for UCX843A,
(VCC =
14 V for UCX842A) Operating
Power Supply Zener Voltage (ICC = 25 mA)
ICC
–
–
VZ
30
0.5
12
36
1.0
17
–
–
–
30
0.5
12
36
1.0
17
–
V
mA
%
DCmax
DCmin
94
–
96
–
–
0
94
–
96
–
–
0
Vth
15
7.8
VCC(min)
9.0
7.0
10
7.6
11
8.2
8.5
7.0
10
7.6
11.5
8.2
16
8.4
17
9.0
14.5
7.8
16
8.4
17.5
9.0
V
V
V
VOL
VOH
VOL(UVLO)
–
tr
tf
–
–
0.1
50
50
1.1
150
150
–
–
–
0.1
50
50
1.1
150
150
ns
ns
–
–
13
12
0.1
1.6
13.5
13.4
0.4
2.2
–
–
–
–
13
12
0.1
1.6
13.5
13.4
0.4
2.2
–
–
V
AV
Vth
PSRR
–
IIB
tPLH(in/out)
–
–
70
–2.0
150
–
–10
300
–
–
–
70
–2.0
150
–
–10
300
µA
ns
2.85
0.9
3.0
1.0
3.15
1.1
2.85
0.9
3.0
1.0
3.15
1.1
V/V
V
dB
VFB
IIB
AVOL
BW
PSRR
ISink
ISource
VOH
VOL
2.45
–
65
0.7
60
2.0
–0.5
5.0
–
2.5
–0.1
90
1.0
70
12
–1.0
6.2
0.8
2.55
–1.0
–
–
–
–
–
–
1.1
2.42
–
65
0.7
60
2.0
–0.5
5.0
–
2.5
–0.1
90
1.0
70
12
–1.0
6.2
0.8
2.58
–2.0
–
–
–
–
–
V
–
1.1
V
µA
dB
MHz
dB
mA
Symbol
Min
Typ
Max
Min
UC384XA
Typ
Max
Unit
NOTES:
2. Adjust VCC above the Startup threshold before setting to 15 V.
3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible
Tlow =
–20°C
for UC3842A, UC3843A
Thigh = +70°C for UC3842A, UC3843A
Tlow =
–25°C for UC2842A, UC2843A
Thigh =
+85°C for UC2842A, UC2843A
4. This parameter is measured at the latch trip point with VFB = 0 V.
∆V
Output Compensation
5. Comparator gain is defined as: AV
∆V
Current Sense Input
MOTOROLA ANALOG IC DEVICE DATA
3
UC3842A, 43A UC2842A, 43A
Figure 1. Timing Resistor versus
Oscillator Frequency
80
50
RT, TIMING RESISTOR (k
Ω
)
20
8.0
5.0
2.0 VCC = 15 V
TA = 25°C
0.8
10 k
20 k
50 k
100 k
200 k
500 k
1.0 M
% DT, PERCENT OUTPUT DEADTIME
100
50
20
10
5.0
2.0
1.0
VCC = 15 V
TA = 25°C
Figure 2. Output Deadtime versus
Oscillator Frequency
10 k
20 k
50 k
100 k
200 k
500 k
1.0 M
fOSC, OSCILLATOR FREQUENCY (Hz)
fOSC, OSCILLATOR FREQUENCY (Hz)
Figure 3. Oscillator Discharge Current
versus Temperature
9.0
I dischg , DISCHARGE CURRENT (mA)
VCC = 15 V
VOSC = 2.0 V
8.5
Dmax , MAXIMUM OUTPUT DUTY CYCLE (%)
100
90
80
70
60
50
40
800
Figure 4. Maximum Output Duty Cycle
versus Timing Resistor
VCC = 15 V
CT = 3.3 nF
TA = 25°C
Idischg = 7.2 mA
8.0
7.5
Idischg = 9.5 mA
1.0 k
2.0 k
3.0 k
4.0 k
6.0 k
8.0 k
7.0
–55
–25
0
25
50
75
TA, AMBIENT TEMPERATURE (°C)
100
125
RT, TIMING RESISTOR (Ω)
Figure 5. Error Amp Small Signal
Transient Response
VCC = 15 V
AV = –1.0
TA = 25°C
Figure 6. Error Amp Large Signal
Transient Response
VCC = 15 V
AV = –1.0
TA = 25°C
2.55 V
3.0 V
20 mV/DIV
2.5 V
2.5 V
2.45 V
0.5
µs/DIV
2.0 V
0.1
µs/DIV
4
MOTOROLA ANALOG IC DEVICE DATA
200 mV/DIV
UC3842A, 43A UC2842A, 43A
Figure 7. Error Amp Open Loop Gain and
Phase versus Frequency
A VOL , OPEN LOOP VOLTAGE GAIN (dB)
100
80
Gain
60
40
Phase
20
0
120
150
100
1.0 k
10 k
100 k
1.0 M
180
10 M
VCC = 15 V
VO = 2.0 V to 4.0 V
RL = 100 K
TA = 25°C
Vth, CURRENT SENSE INPUT THRESHOLD (V)
0
30
60
90
φ
EXCESS PHASE (DEGREES)
,
1.2
VCC = 15 V
1.0
0.8
0.6
TA = 125°C
0.4
0.2
0
TA = –55°C
TA = 25°C
Figure 8. Current Sense Input Threshold
versus Error Amp Output Voltage
– 20
10
0
f, FREQUENCY (Hz)
2.0
4.0
6.0
VO, ERROR AMP OUTPUT VOLTAGE (V)
8.0
ISC, REFERENCE SHORT CIRCUIT CURRENT (mA)
∆
V ref , REFERENCE VOLTAGE CHANGE (mV)
Figure 9. Reference Voltage Change
versus Source Current
0
VCC = 15 V
Figure 10. Reference Short Circuit Current
versus Temperature
110
VCC = 15 V
RL
≤
0.1
Ω
90
–4.0
–8.0
–12
–16
–20
–24
0
20
40
60
80
100
120
Iref, REFERENCE SOURCE CURRENT (mA)
TA = 125°C
TA = 25°C
70
TA = 55°C
50
–55
–25
0
25
50
75
100
125
TA, AMBIENT TEMPERATURE (°C)
, OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)
VCC = 15 V
IO = 1.0 mA to 20 mA
TA = 25°C
, OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)
Figure 11. Reference Load Regulation
Figure 12. Reference Line Regulation
VCC = 12 V to 25 V
TA = 25°C
O
∆
V
2.0 ms/DIV
∆
V
MOTOROLA ANALOG IC DEVICE DATA
O
2.0 ms/DIV
5
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